A bladder is an independently saleable commodity. If it is employed in medical applications for gas transfusion etc., it can be employed without any outer cover thereon. However, if it is employed in sport industry for manufacture of balls, particularly for inflatable balls, then it is covered with an outer cover to protect it from bursting and to form a ball. The outer cover is either hand stitched or machine stitched depending upon the game in which it is being used or the desired characteristics and quality of the end product. The hand stitched outer cover is required, for example, in match and practice balls, and machine stitched cover is required, for example, in match and practice balls including promotional balls wherein the volume of demand is relatively higher. The term promotional balls means the balls used by manufacturers and/or promoters to promote their products and events, such as during trade fairs, national games, international games, etc. The physical characteristics of bladder for both types of outer covers are different.
The present invention particularly relates to a carboxylated acrylonitrile butadiene latex seamless bladder, which is particularly suitable for hand stitched inflatable balls. However, it may be understood that the scope of present invention is not restricted by use of disclosed seamless bladder for hand stitched inflatable balls, because surprisingly the present bladder being suitable for hand stitched inflatable balls has also been found suitable for machine stitched balls including, but not limited to inflatable balls, and also for medical applications including gas transfusion.
For inflatable balls, the film for manufacturing a bladder is not only required to be of suitable weight, but is also required to have controlled inflation capability when inflated as a bladder, to give required shape and size of the ball and to protect the bladder made from such film as well as the outer cover from de-shaping and bursting on inflation.
On the contrary, for medical applications, such as for manufacturing hand gloves, the film for manufacturing the gloves is neither required to be of a suitable weight nor required to have controlled inflation capability as it is neither required to have bounce characteristics nor to be inflated as a bladder to have a particular shape and size, nor is required to be protected from de-shaping and bursting on inflation.
It has been observed that for manufacturing a hand glove, even a very lighter film having weight varying from about 100 to about 200 mg/inch2 is sufficient because, as stated, it is neither required to have any bounce characteristics nor to have a shape as in case of a ball. Further, the glove is not required to be stitched to any outer cover.
On the contrary, it has been observed that for hand stitched inflatable balls, the film for manufacturing a bladder is required to have relatively very heavy weight varying from about 500 to about 700 mg/inch2, which has been found suitable for providing the shape and bounce characteristics to the hand stitched balls, because the outer cover of the ball and its stitches are strong enough.
Similarly, for machine stitched inflatable balls, it has been observed that the film for manufacturing a bladder is required to have even further heavier weight varying from about 700 mg/inch2 to about 1.5 g/inch2, which has been found suitable for providing the shape and bounce characteristics to the machine stitched balls, because the outer cover of such balls and its stitches are not strong enough as compared to hand stitched balls.
Therefore, a film used for manufacturing a hand glove cannot be employed for manufacturing a bladder suitable for a ball.
It has been further observed that in conventional balls, if bladder is not made of a film having a required weight and controlled inflation capability, the required weight and controlled inflation capability is, then, generally achieved by applying one or more layers of thread breading around the outer layer of the bladder, which has been found to result in increase in the hardness of the bladder, and hence, the bladder does not remain suitable for playing football, and additionally it looses its spherical shape.
In conventionally available inflatable balls, the bladder made from butyl rubber is used. However, such bladders are not of required weight. In case of butyl rubber bladders, the required weight is achieved by increasing its wall thickness which is determined based on the weight required by employing molding process which is conventionally carried out on an unsupported film made by pasting four panels and not on a bladder per se.
The major problem of manufacturing a butyl rubber bladder having required weight by increasing its wall thickness by molding is that the cost of material increases manifold.
Further, the major problem of the molding process is that it cannot be employed if a seamless bladder is required. As present invention aims of providing a seamless bladder, the molding process, therefore, is not suitable.
Still further problem of molding process is that even the joints are not of uniform weight, that is, weight at the joints of the bladder is relatively higher adversely resulting in wobbling effect during flight of the ball.
Yet another problem of molding process is that it has been found to be more expensive, and yet resulting in higher rejection, and hence, effectively lower production rate with higher capital cost.
Further, it has been observed that even by manufacturing the butyl rubber bladder by molding process, the required weight cannot be achieved. Therefore, in case of conventionally available bladders thread breading of nylon fiber around butyl bladder is applied to achieve the desired weight characteristics, which has been found to enhance controlled inflation capability of the bladder produced, but as stated herein, the thread breading results in increase in the hardness of the bladder, and hence, makes it unsuitable for playing football, and additionally loss of its spherical shape.
In U.S. Pat. No. 4,191,375, issued on Mar. 4, 1980, a game ball having an inner bladder provided with a layer of yarn fiber is discussed.
The U.S. Pat. No. 4,830,373, issued to Dehnert et al, describes a soccer ball which includes an inflatable floating bladder comprising two ply of butyl within a thread form of carcass.
The U.S. Pat. Nos. 5,772,545 and 6,390,941 B1 issued to Ou describe use of strengthened nylon thread overlapping each other to form a web like layer which permanently embraces and adheres to the bladder and supports the outer cover of the ball.
The U.S. Pat. No. 6,793,597 describes machine stitched ball with floating bladder. It consists of bladder and the outer cover wherein the outer cover is vulcanized with web of thread and adhesive. Further, the outer surface of the bladder is coated with the silicone releasing chemical before winding.
However, it has been observed that the fiber is applied around outer layer of the bladder in the form of a web like structure which does not allow bladder to inflate more than it has initially inflated for the purpose of breading by nylon fiber. Therefore, such bladders suffer from problem of limited inflation.
Further, as stated herein, it has been observed that due to thread breading, the bladder becomes harder, which limits its applications and wide acceptability because harder is the bladder, the players are hit harder during playing, for example, while kicking, heading etc. This problem can be overcome, but by providing additional padding between thread breading of the bladder and outer cover of the ball, which in-turn adds on the cost of the end product-ball, and hence make it commercially unviable.
Further, when a bladder is used in sports industry, it is desired that it should have judicious combination of bounce as well as air retention characteristics without sacrificing one property for the another property.
It has been observed that bladders made from synthetic butyl rubber exhibit good air retention characteristics, but have poor bounce characteristics. Such bladders have been accepted, but the need for seamless bladder having judicious combination of good air retention characteristics and good bounce characteristics, and still having low manufacturing cost, high productivity and low rejection rate has not been satisfied.
Further, the bladders made from natural rubber exhibit good bounce characteristics, but have poor air retention characteristics. Such bladders have also been accepted, but the need for seamless bladder having judicious combination of good air retention characteristics and good bounce characteristics, and still having high productivity and low rejection rate has not been satisfied.
It has been observed that even the bladders made from conventionally used synthetic latex exhibit good air retention characteristics, but have poor bounce characteristics.
Further, it has been observed by the inventors of the present invention that when a bladder is made from synthetic latex, particularly from synthetic acrylonitrile butadiene latex, the processability of the synthetic latex to have a film of desired thickness and weight is not possible.
It has been found that bladders made from synthetic acrylonitrile butadiene latex film are of thickness varying up to about 0.20 mm. The main drawback of a film of synthetic acrylonitrile butadiene latex having such a lower thickness is that stripping of film becomes very difficult.
Further, the inventors of the present invention have found that if a film of synthetic acrylonitrile butadiene latex for manufacture of a bladder having thickness more than about 0.25 mm is achieved, then drying problem is observed during manufacture of a film which in-turn has been found to cause cracks in the film.
It has been further found that bladders made from synthetic acrylonitrile butadiene latex film are of weight varying up to about 300 mg/inch2, which as described herein, have not been found suitable for providing the shape and bounce characteristics even of the hand stitched balls, because as described herein, a film to manufacture a bladder suitable for hand stitched inflatable balls should have relatively very heavy weight varying from about 500 to about 700 mg/inch2 and for machine stitched inflatable balls should have even further heavier weight varying from about 700 mg/inch2 to about 1.5 g/inch2.
Still another problem observed with synthetic acrylonitrile butadiene latex is that it results in a film having modulus varying from about 10 to 12 Kg/Cm2 at 100% stretch [or elongation], which has been found to be a main cause of resulting in a bladder having poor bounce characteristics.
Yet another problem observed with synthetic acrylonitrile butadiene latex is that it results in a film having poor cross-linking as found by measuring tensile strength which has been found to be varying from 60 to 70 kg/cm2 and elongation at break which has been found to be varying from 450 to 500%. Such a poor cross-linking has been found to be another cause of resulting in a bladder having poor bounce characteristics as well as reduced air retention characteristics.
Even further it has been observed that bladder made from film of synthetic acrylonitrile butadiene latex gets tear-off from its neck during stripping from a mould resulting in total loss of production.
Further, such bladders made from conventionally used synthetic latex do not have required bounce and controlled inflation characteristics. Therefore, such bladders have not been commercially acceptable.
Therefore, it can be concluded that the conventionally used synthetic latex, particularly the synthetic acrylonitrile butadiene latex is not suitable for manufacturing a film suitable for manufacturing a bladder for inflatable balls.
Further, the bladders made from natural latex exhibit good bounce characteristics, but have poor air retention characteristics. Such bladders have been accepted, but the need for a bladder having judicious combination of good air retention characteristics and good bounce characteristics, and still having low manufacturing cost, high productivity and low rejection rate has not been satisfied.
Accordingly, it has been found that when conventionally available bladders are made either from conventionally used synthetic rubber or synthetic latex, or from conventionally used natural rubber or natural latex, these have either poor air retention characteristics or poor bounce characteristics. Therefore, neither the bladders made from conventionally used synthetic rubber or synthetic latex, nor the bladders made from conventionally used natural rubber or natural latex have been commercially acceptable.
Therefore, a need to have a bladder having judicious combination of bounce characteristics as well as air retention characteristics, and controlled inflation capability without sacrificing one property for the another property has been felt for an inflatable ball.
An attempt has been made to manufacture bladders by employing blends of natural rubber and synthetic rubber.
However, it has been found that even bladders made from blends of natural rubber and synthetic-rubber suffer primarily from poor curing, i.e. cross linking, which in-turn results in low bounce characteristics. Even blends of synthetic rubber with natural rubber have not been able to result in a bladder having good bounce as well as good air retention characteristics.
Another problem of bladders made from blends of natural rubber and synthetic rubber is that these are not seamless as these are made by employing molding process, and hence, do not have uniform weight over the entire area, which in-turn results in an inflatable ball having wobbling effects, and therefore, higher rejection rate of the bladders and balls made therefrom.
Still another attempt has been made to manufacture bladders by employing blends of natural latex and synthetic latex, wherein such bladders are manufactured by employing dipping process, and wherein synthetic latex is selected from a group consisting of synthetic acrylonitrile butadiene latex, neoprene [for example polychloroprene latex], isoprene [for example, polyisoprene latex], SBR [styrene butadiene rubber] and natural latex is commonly known as centrifuged latex.
However, it has been found that even bladders made from blends of natural latex and synthetic latex suffer primarily from poor curing, i.e. cross linking, which in-turn results in low bounce characteristics. Even blends of synthetic latex with natural latex have not been able to result in a bladder having good bounce as well as good air retention characteristics.
Accordingly, it has been found that when conventionally available bladders are made either from blends of natural rubber and synthetic rubber or from blends of natural latex and synthetic latex, these have poor curing, and hence, have poor bounce characteristics, and in-addition bladders made from blends of natural rubber and synthetic rubber are not seamless bladders. Therefore, neither the bladders made from natural rubber and synthetic rubber nor the bladders made from natural latex and synthetic latex have not been acceptable, because these bladders also lack judicious combination of good air retention characteristics and good bounce characteristics.
Yet another attempt has been made to manufacture bladders by employing laminates of natural latex and synthetic latex, wherein synthetic latex is selected from a group consisting of synthetic acrylonitrile butadiene latex, neoprene [for example polychloroprene latex], isoprene [for example, polyisoprene latex], SBR [styrene butadiene rubber] and natural latex is commonly known as centrifuged latex.
However, it has been found that even bladders made from laminates of natural latex and synthetic latex primarily suffer not only from poor curing, i.e. cross linking, which in-turn results in low bounce characteristics, but also from problem of delamination of layers of the laminate, which in-turn results in bursting during performance, and hence, further rejection of the bladder. Accordingly, even laminates of natural latex and synthetic latex have not been able to result in a bladder having good bounce as well as good air retention characteristics, and good strength of the laminate per se to result in strong enough bladder.
Therefore, it has been found that even the bladders made from laminates of natural latex and synthetic latex have not been commercially acceptable.
Even another attempt to manufacture bladders by employing laminates of natural rubber and synthetic rubber has not been commercially successful.
It has been found that even bladders made from laminates of natural rubber and synthetic rubber primarily suffer not only from poor curing, i.e. cross linking, which in-turn results in low bounce characteristics, but also from problem of delamination of layers of the laminate, which in-turn results in bursting during performance, and further rejection of the bladder. Accordingly, even laminates of natural rubber and synthetic rubber have not been able to result in a bladder having good bounce as well as good air retention characteristics, and good strength of the laminate per se to result in strong enough bladder.